# std::chrono::operator<<(std::chrono::year_month_day)

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< cpp‎ | chrono‎ | year month day

Defined in header `<chrono>` |  |
template< class CharT, class Traits > std::basic_ostream<CharT, Traits>& operator<<( std::basic_ostream<CharT, Traits>& os, const std::chrono::year_month_day& ymd ); |  | (since C++20)

Outputs a textual representation of ymd into the stream os. This first forms a std::basic_string<CharT> s consisting of a textual representation of the date in the format `yyyy-mm-dd` (same as the one output by `formatter` with the %F specifier). Then, if !ymd.ok(), appends " is not a valid date" to `s`. Inserts `s` into os.

Equivalent to

return os << (ymd.ok() ?
std::format(STATICALLY_WIDEN<CharT>("{:%F}"), ymd) :
std::format(STATICALLY_WIDEN<CharT>("{:%F} is not a valid date"), ymd));

where STATICALLY_WIDEN<CharT>("...") is "..." if `CharT` is char, and L"..." if `CharT` is wchar_t.

### Return value

os

### Example

| This section is incomplete Reason: no example

### See also

format (C++20) | stores formatted representation of the arguments in a new string (function template)
std::formatter<std::chrono::year_month_day> (C++20) | formatting support for `year_month_day` (class template specialization)

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